It depends what you want to achieve. Most of the time specular and diffuse should be (1.0, 1.0, 1.0), because proper brightness and colorization of your model should be done by texture.
Shinniness however is how much specular light will spread over the surface: small value around 15 - specular will be spread, big value around 250 - you will very narrow and hard-edged circle of specular lighting.
However if you are new to 3D and working with game models then I suggest you to read some basics. Phong shading model should give you some insight of one type of lighting in 3d graphics: https://en.wikipedia.org/wiki/Phong_reflection_model
This is more or less principle of lighting in scs games and from that you should get idea of what ambient, diffuse and specular does. Now how exactly shaders work in our games that's another story and you might read this:http://modding.scssoft.com/wiki/Documen ... ed_shaders
Also don't forget to search this forums I know that somewhere there was nice explanation from abasstrepass about how he uses materials in his models.